Accurate measurement is critical for precision CNC machined parts, the micrometer is a common measuring tool for mechanical parts. In this article, from the definition of micrometer, follow us to learn about the types and basic parts of a micrometer, more importantly, fast to get the micrometer reading and measuring method.
A micrometer, also known as the micrometer screw gauge, is a precision measurement device with a calibrated screw mainly used to measure small distances or thickness between two faces of the mechanical engineering and machining parts, it is often used along with other metrological instruments like dial, vernier, and digital calipers. Micrometer is also a useful tool for apparent diameter measurement of celestial bodies or microscopic objects in telescopes or microscopes.
Types of micrometer
– Outside micrometer: designed for measuring the outside of objects—the outside diameter (OD).
– Inside micrometer: measure the inside, or inside diameter (ID)
– Depth micrometer: measure the depth of a hole, recess or slot
Learn about the construction and mechanism of the instrument for better understanding and proper use of a micrometer. The main parts of a micrometer with its function are as below.
– Anvil: stationary cylindrical part, one of the two holding points for objects to be measured
– Spindle: moveable cylindrical and long part connect with ratchet, another holding point, to suit the size of the part
– Lock nut: works as stationary nut, hold the mechanism firmly and resist loosening under vibrations and torque
– Zero adjust screw: correct or adjust the zero error
– C-frame: a c-shaped frame, works as a rigid part with both holding or fixing points (anvil and sleeve)
– Sleeve: with the main scale, indicates the reading in millimeter in case of the imperial micrometer
– Thimble: with rotating vernier scale, show the measurement value in fraction
– Knurled Gripe:
– Ratchet: limits applied pressure by slipping at a calibrated torque
There is not only one method to read micrometers.
1. Check the whether micrometer in English or metric, ensure the tool use the same unit as the measurement device
2. Rotate your micrometer into a proper position and measure the object
3. Read the largest number and count the number of quarters shown on the sleeve first, then read the number is aligned with the datum line on the thimble. Finally, add together these two numbers. The sleeve can be regarded as a ruler with ten numbers, and the space between each number is divided into quarters. One the sleeve, 1 corresponds to .100 inches, one quarter means .025 inches; while on the thimble, each line is equal to .001 inch, for example, 11 is read as 0.011 inches.
(You can think of the markings on the sleeve as dollars and quarters, 1 means one dollar and a quarter means 25 cents. And the numbers on thimble present cents, 10 means 10 cents. Convert the final result to inches, such as 2 dollars 35 cents is 0.235 inches. )
1. Hold the micrometer in your dominant hand, support the device weight in your palm
2. Grasp the thimble between your thumb and index fingers
3. Partially wrap your pinky or ring finger within the inside of the frame, do not block the object to be measured
4. Hold the part to be measured in another hand
5. Gently pinch the object between the anvil and spindle
6. Twist the ratchet until the object is held firmly
7. Read the micrometer